U.S. Secretary of State John Kerry has sought to reassure Tehran that the White House can waive new visa requirements that have outraged Iranians, but has faced a backlash from Republican leaders in Congress.

Iranian Foreign Minister Mohammad Javad Zarif has complained that the restrictions contradict provisions of the July nuclear accord aimed at lifting economic and travel restrictions on most Iranians in exchange for curbs on Tehran's nuclear activities.

Iranian leaders, with some support from European officials, contend the new rules will scare off potential investors in Iran and tourists from the United States, who would be required to get visas in the future.

But Kerry told Zarif in a December 19 letter that the United States can encourage economic exchanges by issuing waivers and long-term business visas for investors and businessmen who travel frequently to Iran.

“I am...confident that the recent changes in visa requirements passed in Congress, which the Administration has the authority to waive, will not in any way prevent us from meeting our [nuclear deal] commitments, and that we will implement them so as not to interfere with legitimate business interests of Iran,” he said.

“To this end, we have a number of potential tools available to us, including multiple entry ten-year business visas, programs for expediting business visas, and the waiver authority provided under the new legislation,” he wrote.

Kerry's reassurances to Tehran have provoked a backlash in Congress, however, with Republican leaders insisting that the new visa requirements must be strictly followed.

They say the law allows visa waivers for military and official government travel to Iran and three other countries -- Iraq, Syria, and Sudan -- but not for business travel. Republican aides say the Homeland Security Department sought a business exception in negotiations over the legislation, but lawmakers rebuffed the request.

“We are deeply concerned that the narrowly intended use of the waiver authority will be ignored,” wrote House Majority Leader Kevin McCarthy, House Foreign Affairs Committee Chairman Ed Royce, and other Republican leaders in a December 23 letter to the administration.

"This letter serves to dispel any notion that the congressional intent would allow the waiver authority to be used for business travels," they wrote.

McCarthy added separately that “instead of undermining Congressional intent regarding the visa waiver program, the White House should instead focus on Iran’s repeated violations of the UN Security Council's bans on missile tests.... Iran’s unwillingness to follow these international agreements should be a red flag that the Iran nuclear deal isn’t worth the paper it is written on.”

Given the rigid stance taken by Republicans, who uniformly opposed the nuclear deal, Iranian leaders as well as some Iranian American activists have questioned whether the restrictions on travel to Iran were a quiet way for them to sabotage the nuclear deal.

Iranians point out that their citizens were not involved in either of the terror attacks in Paris and California that prompted passage of the legislation last week. But people who were citizens of Saudi Arabia and Pakistan, or who traveled there, were involved in the attacks as well as earlier incidents including the September 11, 2001, terrorist attacks, and yet they are not subject to the new visa restrictions.

Lawmakers say the restrictions on Iran were enacted because of its status as a state sponsor of terrorism.